1. Field of the Invention manually rotating a rotatable shaft such as a rotatable shaft or a roller used to feed a sheet of paper in a printer.
2. Description of the Prior Art
FIG. 1 shows a prior art connection mechanism of a manually operated knob 50 made of a plastic material and employed in a sheet feed apparatus of a printer. The numeral 51 denotes a platen roller; the numeral 52 denotes a rotatable shaft of the platen roller 51; the numeral 53 denotes a grip for manually operating knob 50; and the numeral 54 denotes a cylinder portion coaxially extending from the grip 53. A part of the external surface of rotatable shaft 52 is cut to form a flat surface 56. Cylinder portion 54 has a hole whose cross-section is approximately of the same shape as the cross-section of rotatable shaft 52. A slit 58 extending along the axial direction is provided on the round side of the hole opposite from flat portion 57. Slit 58 permits the cylinder portion 54 to elastically expand to allow insertion of the rotatable shaft 52 therein.
Current printers increasingly have employed a driving method which does not use a clutch between a drive motor and the platen roller. In most cases a stepping motor is used as a sheet-feed motor which is connected via a gear to the platen roller. A stepping motor inherently stays, i.e. locks, at a certain angular position when not being rotationally driven. Therefore, manual rotation of the platen roller 51 to feed a sheet requires a torque to overcome the locking force of the stepping motor. Accordingly, the manual knob must withstand larger torque forces than the conventional knob employed together with a clutch.
In attempting to rotate grip 53 of the prior art structure knob, however, a crack 60 often occurs at a corner 59 between flat portion 57 and round cylindrical portion 54 as shown in FIG. 2. Accordingly, there is a need to provide a durable knob which will withstand cracking by rotational operation.